High-speed inverted object detector

ABSTRACT

This inverted object detector and reject mechanism operates by detecting the difference in reflected light from a correctly oriented can body and an inverted can body. A lens system conducts reflected light from a can onto a photocell. An electrical system takes the photocell output and may convert it into a reject movement, depending upon the reflected light.

United States Patent [191 Stock et al. 1451 Jan. 2, 1973 s41 HIGH-SPEED INVERTED OBJECT 3,097,744 7/1963 Hutter ..2s0/223 DETECTOR 2,070,339 2/1937 Moore ...2s0 223 2,880,328 3/1959 Nordquist ..250/223 [75] Inventors- Mlchae' Oak Lawn 3,003,629 10/1961 Henderson ..209/111.7 chlcagm 3,430,766 3/1969 Stone ..209/111.7 73 Assignee; Continental c Company Inc" 3,532,215 10/1970 Davidson ..209/111.7

New York, NY. Primary Examiner-James W. Lawrence [22] 1970 Assistant Examiner-D. C. Nelms [21] Appl. No.: 66,311 AttorneyAmericus Mitchell, Joseph E. Kerwin and William A. Dittmann [52] US. Cl. ..2S0/223 R, 209/111.7, 250/219 D 51 Int. Cl .1101 39/12 [57] ABSTRACT [58] Field of Search ...250/226, 223, 219; 209/ 111.6, This inverted object detector and reject mechanism 0 45 operates by detecting the difference in reflected light from a correctly oriented can body and an inverted References Cited can body. A lens system conducts reflected light from UNITED STATES PATENTS a can onto a photocell. An electncal system takes the photocell output and may convert 1t into a re ect 3,004,465 10/1961 White movement, depending upon the reflected light. 3,133,201 5/1964 Rock 3,128,879 4/1964 Birchall 5 Claims, 3 Drawing Figures.

AMPLlFlER VARIABLE GAIN AMPLIFIER FIXED GAIN BA N D PASS FILTER TRANSFORMER COUPLlNG DISCRIMINATOR WAIENTEDMHI B 3.708.679

SHEET 1 OF 3 AMPLIFIER FIXED 6mm TRANSFORMER COUPLING DISCRIMINATOR .INVENTORS MICHAEL .1. STOCK G w JOHN R. KOTAL 1 BY 747 M PATENTEDJM 2mm 3.708.679

SHEET 3 UP 3 /(MMMM AMPLIFIED SIGNAL U V U U V U \j V WED a 4 n n "m (x A A in 2 7I 4 64 n nn-Hhm H H UNIJUNCTION OUTPUT & SCR GATE PULSE VOLTAGE ACROSS SCR II RELAY ZED. RELAY TIMING RELAY! INVENTORS MICHAEL J. STOCK ATT' Y.

HIGH-SPEED INVERTED OBJECT DETECTOR Our invention relates to an inverted object detector and most particularly to a detector system for detecting and rejecting inverted can bodies or similar objects on an assembly line.

Up to this time the inspection and rejection system for cans or like objects has been to a high degree manual in operation. Inspection personnel are stationed at points along a conveyor belt where cans or similar objects are passing. These persons lift off inverted cans. This system is inadequate in that the work becomes tedious and the inspectorsattention strays from time to time. Thus, invertedcans sometimes slip through and these cans are not discovered until they have had a self-opening top seamed onto the incorrect end. Such cans have to be scrapped wasting both a can body and an end unit. If the inverted body can be detected before the end unit is attached, both the can body and end unit are saved.

It is an object of this invention to provide a high speed object inspection apparatus for inspecting in dividual objects.

It is another object of this invention to provide a control mechanism for rejecting inverted objects on a conveyor line.

It is a final object of this invention to provide a means for rejecting inverted objects on a high speed conveyor line.

In brief, our apparatus distinguishes an inverted object from an object mounted in an upright position on a conveyor line. The object must have different reflective characteristics at each end. An inverted object may be rejected from the conveyor or righted on the conveyor line. Our apparatus consists of a DC light source which directs light onto the object being inspected. A lens system scans a limited section of this object and transmits a reduced image of the section to a photocell. A light interrupter allows the reflected light to pass from the object to the photocell at the rate of 720 Hertz. This signal is converted into a reject signal via an electrical system. The reflected light intensity is made sinusoidal in character and the electric pulses are conducted from the photocell to an amplifier and from an amplifier to an output level discriminator. A signal from a correctly oriented object produces no result while a signal from an inverted object initiates control action to reject the object.

Other objects and advantages of this invention will become apparent by reference to the accompanying drawing and the specification which follows:

FIG. 1 shows a schematic diagram of our invention.

FIG. 2 shows a diagram of the transformer, discriminator and relay circuits,

FIG. 3 shows a current and voltage diagram taken at various points of the circuit shown in FIG. 2.

This device is of particular utility where cans or similar objects have different reflective characteristics at different levels of the object.

Light from a constant intensity source 1, preferably a quartz iodine bulb, is directed to fall on the side of a can 2 which is mounted on a conveyor 3. The light source may generate a mono-chromatic light or a light having many colors. The conveyor transports the can past the inspection station. Light 4 is reflected from the illuminated can and passes through an ambient light shield 5 and a lens system 6 to form a miniature image on a photocell 7. The constant intensity light source and lens system are mounted so that at no time during the objects transport into, through and out of the inspection area does the specular or direct reflection from the object fall onto the photo sensitive area of the device.

For the particular case of sensing a cylindrical object, the above conditions are best met if the center of said light source is mounted so that when the axis of the cylinder intersects the optical axis of the lens system the light source is in the plane containing both axes. Within this plane the light source is niounted at such an angle that the specular reflection does not fall upon the photocell under normal transport conditions. For this reason, the light source is mounted above or below the optical axis (FIG. 1) about 30-45.

The voltaic photocell may be a selenium cell for example, but the photodevice may be varied depending upon the reflection to be differentiated and the lighting conditions.

The reflected light coming from the object varies in intensity depending upon the characteristics of the portion of the object which is being scanned. Depending .on the reflection, the intensity produces a different voltage response in the photocell. For example, a photocell monitoring a light colored material under the constant light source responds with a different electrical output than does a photocell monitoring, say, a black object. Since a constant intensity light source is used the variation of voltage output from the AC amplifier ,varies according to the intensity level and wave lengths of the light reflected from the can.

The reflected light from the can falls onto the photocell. The reflected light usually consists of many spectral wave lengths because of the types of lithography and the various colors found on a can. The photodevice response is usually different for different colors at the top and bottom of a can. However, if the colors are different and the photodevices response is the same for the two colors then an optical filter may be used to enhance differentiation.

Since the photodevice scans a predetermined area, the majority reflective characteristic is what affects the output the most. For example, if percent of the area is black and 15 percent is white, the electrical signal level is different than if the area was percent black.

Our device has a viewing area of substantial size. We are looking at a particular band of the can, chosen so that the signal differs depending on whether an upright or inverted can is viewed. The signal is such that an output level can be chosen for which the voltage from the photocell is above this level for'one end ofthe can independent of its rotation, and is below this level for the other end independent of its rotation.

By looking at an area, we are able to obtain the average light value reflected from the viewed area. Thus, we can differentiate for example between the white surface and a surface that has blue dots over a white background.

The side seam area of the can which normally has similar reflective characteristics at both ends is made a small part of the sensed area by viewing across almost the entire width of the can.

The frequency of the interrupter is below the saturation limit of response of the photocell, but is constant and chosen sufficiently high so that a can, even if travelling at the fastest transport speed, does not pass by the threshold field of view in the time interval for one interrupting cycle. The threshold field of view is that scanned portion of the can which must be sensed for the photocell to distinguish between the ends. The frequency of the interrupter determines the portion of the photocell frequency response curve (exposure time vs. voltage) at which the photocell is operating. This allows use of the portion of the photocell frequency response curve that gives less than the maximum photocell output for a given light intensity. By chopping the diffuse reflected light at a constant speed, we allow the photocell to view the can or background for precise increments of time. This time is not long enough to allow the photocell to reach its full output, but since the chopping frequency is constant, the voltage output level attained by the photocell is still dependent on the characteristics of the light reflected from the object or background. This in turn allows detection of objects at the speed of a can line as long as the interruption frequency is sufficiently high to insure several photocell exposures to a given can.

The light which passes through the ambient light shield 5 and lens system 6 may be interrupted by a light interrupter 8 or disc. In this embodiment, the interrupter is a disc having slots 9 equally spaced around its edge. The speedof the motor 10 which drives the disc must be such that a few holes allow light rays to pass during the time that each can is at the inspection station. The speed must be very nearly constant. The slots in the disc may be truncated pie sections of equal spacing and of width equal to the lens opening, and thus the light which is allowed to pass has an intensity which is of an approximately sinusoidal nature. This light falls on a photocell 7 and generates an alternating voltage. The alternating voltage caused by the miniature image on the photocell is conducted to an amplifier 11. This amplifier is a variable gain amplifier'to allow adjusting for different signal levels from the cell. The voltage level is raised and the output is connected to a band pass filter 12. This filter is set to pass only the altemating current frequency derived from the interrupter. The voltage level which is passed through the band pass filter is next conducted to a fixed gain amplifier 13. The fixed gain amplifier is the final stage of amplification. The output of the fixed gain amplifier 13 is now coupled by a transformer 14 to the discriminator circuit 15. The output level discriminator 15 is set to trigger a control output reject mechanism 16 if the signal coming from the illuminated area of the object being inspected is not as required. That is to say, the output level discriminator is set so that the signal falls above or below a certain voltage, depending which end of the can is viewed.

If the can or other object is not on the conveyor belt at all, then no signal will be given to the reject mechanism because the colored background 61 triggers an accept condition. This is because the reflected light from the background 61 is chosen to be a type which produces the same photocell response as the inspected part of a correctly oriented can. The discriminator 15 can be set so that voltages above a given level trigger the mechanism 16. The constant intensity light source may be a 200 watt quartz-iodine bulb, for

example. The light rays may be directed upon the area of the object being examined by a reflector.

The discriminator 15 used in our circuit is shown in FIG. 2. Here the signal input from the fixed gain amplifier 13 is conducted into the discriminator through the primary winding 17 of the transfonner 14. This signal then passes to the secondary winding 18 of the coupling transformer. The signal then is conducted through a diode rectifier 19 which removes the negative portion of the alternating voltage signal. The modified signal is now a half-wave rectified signal and enters theemitter 20 of the unijunction transistor 21. A transistor such as 2N 489B is a transistor of the type intended. When the voltage applied to the emitter exceeds a predetermined level, the unijunction transistor becomes conductive and for the period of time that the voltage exceeds the predetermined level, the unijunction transistor conducts electric current from base 22 to base 23. As soon as the applied voltage is lower than the on level of the particular unijunction transistor 21 the transistor shuts off. The wave produced by the unijunction transistorresembles a square wave shape. When the unijunction transistor 21 is on, gate current is applied to a silicon controlled rectifier 24 such asSCR GE C6B causing it to conduct. The SCR has an anode 25, a cathode 26 and a gate 27. When the SCR is conducting, then the voltage across it drops to a small value. The current through the SCR is derived from a 24 volt AC supply 28 as shown in FIG. 2.

In the SCR circuit, the SCR 24 is connected in series with a high speed relay 29. A reed relay is used in our device. When the SCR conducts current, the contacts of the reed relay 29 close, because the conducted current passes through both the SCR 24 and through the reed relay 29. When reed relay 29 closes, normally open contact points 33, 34 are closed by a connecting mechanism 64.

Since the SCR is connected in a DC circuit it can be switched of only by reducing the current flow through the SCR to zero.

In order to allow the SCR to switch off, a parallel path of negligible resistance for the current is set up around the SCR-This parallel path in effect switches out the SCR when the parallel path contacts areclosed around the SCR and series relay. This path is through the contact points 31, 32 and produces a closed electric circuit. This conductive path exists when the reed relay 29 powered by the SCR 24 actuates contacts 33, 34 and a second or shorting relay 35. The shorting relay 35 has a small time delay capacitor 36 which holds it from being deenergized for about 10 milliseconds.

When the delay relay 35 closes the contacts 31, 32 in the shorting circuit 30 around reed relay 29 and the SCR 24, these shorting contacts are held closed for the time delay. Mechanical connector 65 moves the'normally open contact points 31, 32 to closed position with the relay 35. The SCR 24 is now turned off if there is no gate voltage present. After the contacts open the SCR 24 again starts conducting only when it receives another gate pulse to initiate the cycle indicated above. Reed relay 35 also controls contacts 37, 38 through mechanical connector 66. Contacts 37, 38 are in the circuit 39 with output relay 40. Values of capacitance 41 can be varied for an adjustable time delay which can hold relay 40 actuated. This capacitance 41 is varied to provide time for the container or containers to proceed downstream a predetermined distance before any operation is performed on them. The relay 40 is used to actuate a control function 16 or other device for affecting some condition of the container. The control function 16 may be caused to eject the container from the conveyor line, for example.

Thus, the circuit reacts whenever a high amplitude output from the photocell exceeds the predetermined threshold, unless relay 35 has already been actuated.

Here in this device, there is a control actuation which is held energized for a period of time much longer than the cycle period of the first time delay sequence. The output time delay relay 40 is switched on by the shorting relay 35. When the shorting relay drops out, the output time delay starts timing off. But, if the sequence is started again this output relay is reset to begin its full timing period. The third relay or output relay in our apparatus operates the reject device.

The operation of the circuit is shown most clearly by reference to the circuit output diagram of FIG. 3.

The amplified signal 42 is shown in line A as an output of the coupling transformer 14 and is applied to one side of the diode rectifier 19. The action of the diode rectifier is such that it passes current in one direction only. Thus, only the positive half 43, 44 of the amplified signal is passed beyond the diode rectifier. This amplified half is shown in FIG. 33.

Those signals 43 which are of sufficient amplitude render the unijunction transistor 21 conductive during the period of time that their amplitude exceeds the conducting threshold of the unijunction transistor. A graph representing the unijunction transistor output 45 is shown in FIG. 3C.

This curve, FIG. 3C, also represents or indicates the timing of the SCR gate pulse. That is to say, a gate pulse is applied to the SCR during periods 45 indicated by current above the zero line.

FIG. 3D shows the voltage 46 applied across the SCR. The voltage is dropped by the first output square wave 47 from the unijunction because the SCR- becomes conducting at that time and there is only a small voltage 48 across the SCR. When reed relay 3S feeds back to close the shunt path30 around relay 29 then the SCR 24 stops conducting and there is zero voltage 62 across the SCR.

During the period that the SCR is conducting, current is passed through conductive relay 29. This is a reed relay and the coil voltage 49 of the reed relay is indicated in FIG. 3E.

As mentioned above, the conduction of current I through reed relay 29 causes closing of contacts 33, 34 in the relay circuit 50. Upon closing of these contacts current passes through second relay 35 and it in turn closes the by-pass circuit 30 around conductive relay 29. Relay 35 contacts 31, 32 are held closed'by the time delay capacitor 36 for about 10 milliseconds. Relay 40 in the third circuit 39 is energized at the same time the reed relay circuit 50 is closed. The third relay circuit 39 is held operating for the output time delay period determined by the value of capacitance 41. The period of closure 51, 52 of the second reed relay and the period of closure 53 of the third relay is indicated in FIG. 3F and G respectively.

Resistors 55-60 are biasing resistors.

The advantages of our apparatus are that it can detect inverted objects, operate at a high speed, is highly efficient, discriminates between a variety of reflective characteristics.

The foregoing is a description of our illustrative embodiment of the invention, and it is applicants intention in the appended claims to cover all forms which fall within the scope of the invention.

What is claimed is:

1. A device for determining the orientation of a container having different reflective characteristics at opposed ends comprising:

a light source for developing light of a constant intensity;

a photocell for converting light rays into electric current and having an output terminal, said photocell being mounted out of the line of rays from said light source which are reflected directly from said container;

means for conducting light rays from a selected portion of said container to said photocell;

a light ray interrupter for blocking and alternately permitting the passage of light from said selected portion of said container to said photocell;

a variable amplifier having an input terminal and an output terminal;

electrically conductive means connecting the output of said photocell to the input terminal of said variable amplifier;

a band pass filter for passing impulses of the frequency of said interrupter and having an input terminal and an output terminal;

electrically conductive means connected between the output of said variable amplifier and the input terminal of said band pass filter;

a transformer having a primary coil and a secondary coil;

said primary coil having a first terminal and a second terminal;

said secondary coil having a first terminal and a second terminal;

electrically conductive means connecting the output terminal of said band pass filter to the first terminal of said primary coil;

electrically conductive means connecting the second terminal of said primary coil to ground;

electrically conductive means connecting the second terminal of said secondary coil to ground;

an output discriminator for detecting the presence of a signal indicating that an inverted can is present in the device and having a first input terminal and a second input terminal;

electrically conductive .means connecting the first terminal of said secondary coil means to said first input terminal of said output discriminator; and

electrically conductive means connecting the second input terminal of said secondary coil means to ground.

2. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 1 in which said output discriminator comprises:

rectifier means for eliminating the negative half of an alternating current wave and passing the positive half of said wave and having an input terminal and an output terminal;

electrically conductive means connecting the first terminal of said secondary coil of said transformer to the input of said third electrical means; and

first electrical means electrically connected to the output terminal of said rectifier for differentiating between the signals derived from inverted objects and objects correctly positioned whereby said means actuates further means to alter the position of said inverted object.

3. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 2 in which said first electrical means comprises:

a unijunction transistor having an emitter and a first and a second base;

electrically conductive means connected between the output terminal of said rectifier and the emitter of said unijunction transistor;

a source of voltage;

electrically conductive means connected between said source of voltage and the first base of said unijunction transistor;

second electrical means for amplifying the signals of said transistor and cycling said signals whereby said means actuates further means to alter the position of said inverted object; and

electrically conductive means connected between the second base of said unijunction transistor and said fourth electrical means.

4. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 3 in which said second electrical means comprises:

a silicon controlled rectifier having an anode, a

4 cathode and a gate;

electrically conductive means connecting said gate to the output of the second base of said unijunction transistor;

electrically conductive means connecting said cathode to ground;

a relay circuit having at least a first terminal and a second terminal;

electrically conductive means connecting said first terminal to said anode; and electrically conductive means second terminal to ground.

5. A device for determining the orientation of a container having different reflective characteristics at opposed ends as setforth in claim 4 in which said relay circuit comprises:

a first relay having first and second terminals;

electrically conductive means for connecting said anode of said silicon conductive rectifier to said first terminal of said first relay;

a first biasing resistor having a first and a second terminal;

electrically conductive means connecting the second terminal of said relay to the first terminal of said resistor;

a second source of D. C. voltage having a first and a second terminal;

electrically conductive means connecting the second connecting said terminal of said resistor to the first terminal of said D. C. source; electrically conductive means connecting the second terminal of said D. C. source to ground; a second biasing resistor having a first and a second terminal;

electrically conductive means connecting the first terminal of said second resistor to the first terminal of said first biasing resistor;

a first switch, having first and second normally open electrical contact points;

electrically conductive means connecting said second terminal of said first biasing resistor to said first contact point;

a second relay having first and second terminals;

electrically conductive means connecting said second contact point to the first terminal of said second relay;

electrically conductive means connecting the second terminal of said second relay to ground;

a delaying capacitor having a first and a second terminal;

electrically conductive means connecting said second contact point to the first terminal of said capacitor;

mechanical means connecting said first relay to said first switch to close said contact points when current is conducted through said first relay;

electrically conductive means connecting the second terminal of said capacitor to ground;

a second switch having first and second normally open contact points;

electrically conductive means connecting said second terminal of said first relay to said first contact point of said second switch;

electrically conductive means connecting said second contact point of said second switch to ground;

mechanical means connecting said second relay to said second switch to close said contact points when current is conducted through said second relay;

a third switch having first and second normally open contact points; I

electrically conductive means connecting the first contact point of said third switch to said first terminal of said second D. C. source;

a variable capacitor having a first and a second terminal;

electrically conductive means connecting said first terminal of said capacitor to said second contact point of said third switch;

electrically conductive means connecting second terminal of said capacitor to ground;

a third relay having a first and a second terminal;

electrically conductive means connecting said second contact point of said third switch to said first terminal of said third relay; and

electrically conductive means connecting said second terminal of said third relay to ground whereby when an off color object is detected a motor may be actuated to operate upon the object.

said 

1. A device for determining the orientation of a container having different reflective characteristics at opposed ends comprising: a light source for developing light of a constant intensity; a photocell for converting light rays into electric current and having an output terminal, said photocell being mounted out of the line of rays from said light source which are reflected directly from said container; means for conducting light rays from a selected portion of said container to said photocell; a light ray interrupter for blocking and alternately permitting the passage of light from said selected portion of said container to said photocell; a variable amplifier having an input terminal and an output terminal; electrically conductive means connecting the output of said photocell to the input terminal of said variable amplifier; a band pass filter for passing impulses of the frequency of said interrupter and having an input terminal and an output terminal; electrically conductive means connected between the output of said variable amplifier and the input terminal of said band pass filter; a transformer having a primary coil and a secondary coil; said primary coil having a first terminal and a second terminal; said secondary coil having a first terminal and a second terminal; electrically conductive means connecting the output terminal of said band pass filter to the first terminal of said primary coil; electrically conductive means connecting the second terminal of said primary coil to ground; electrically conductive means connecting the second terminal of said secondary coil to ground; an output discriminator for detecting the presence of a signal indicating that an inverted can is present in the device and having a first input terminal and a second input terminal; electrically conductive means connecting the first terminal of said secondary coil means to said first input terminal of said output discriminator; and electrically conductive means connecting the second input terminal of said secondary coil means to ground.
 2. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 1 in which said output discriminator comprises: rectifier means for eliminating the negative half of an alternating current wave and passing the positive half of said wave and having an input terminal and an output terminal; electrically conductive means connecting the first terminal of said secondary coil of said transformer to the input of said third electrical means; and first electrical means electrically connected to the output terminal of said rectifier for differentiating between the signals derived from inverted objects and objects correctly positioned whereby said means actuates further means to alter the position of said inverted object.
 3. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 2 in which said first electrical means comprises: a unijunction transistor having an emitter and a first and a second base; electrically conductive means connected between the output terminal of said rectifier and the emitter of said unijunction transistor; a source of voltage; electrically conductive means connected between said source of voltage and the first base of said unijunction transistor; second electrical means for amplifying the signals of said transistor and cycling said signals whereby said means actuates further means to alter the position of said inverted object; and electrically conductive means connected between the second base of said unijunction transistor and said fourth electrical means.
 4. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 3 in which said second electrical means comprises: a silicon controlled rectifier having an anode, a cathode and a gate; electrically conductive means connecting said gate to the output of the second base of said unijunction transistor; electrically conductive means connecting said cathode to ground; a relay circuit having at least a first terminal and a second terminal; electrically conductive means connecting said first terminal to said anode; and electrically conductive means connecting said second terminal to ground.
 5. A device for determining the orientation of a container having different reflective characteristics at opposed ends as set forth in claim 4 in which said relay circuit comprises: a first relay having first and second terminals; electrically conductive means for connecting said anode of said silicon conductive rectifier to said first terminal of said first relay; a first biasing resistor having a first and a second terminal; electrically conductive means connecting the second terminal of said relay to the first terminal of said resistor; a second source of D. C. voltage having a first and a second terminal; electrically conductive means connecting the second terminal of said resistor to the first terminal of said D. C. source; ELECTRICALLY conductive means connecting the second terminal of said D. C. source to ground; a second biasing resistor having a first and a second terminal; electrically conductive means connecting the first terminal of said second resistor to the first terminal of said first biasing resistor; a first switch, having first and second normally open electrical contact points; electrically conductive means connecting said second terminal of said first biasing resistor to said first contact point; a second relay having first and second terminals; electrically conductive means connecting said second contact point to the first terminal of said second relay; electrically conductive means connecting the second terminal of said second relay to ground; a delaying capacitor having a first and a second terminal; electrically conductive means connecting said second contact point to the first terminal of said capacitor; mechanical means connecting said first relay to said first switch to close said contact points when current is conducted through said first relay; electrically conductive means connecting the second terminal of said capacitor to ground; a second switch having first and second normally open contact points; electrically conductive means connecting said second terminal of said first relay to said first contact point of said second switch; electrically conductive means connecting said second contact point of said second switch to ground; mechanical means connecting said second relay to said second switch to close said contact points when current is conducted through said second relay; a third switch having first and second normally open contact points; electrically conductive means connecting the first contact point of said third switch to said first terminal of said second D. C. source; a variable capacitor having a first and a second terminal; electrically conductive means connecting said first terminal of said capacitor to said second contact point of said third switch; electrically conductive means connecting said second terminal of said capacitor to ground; a third relay having a first and a second terminal; electrically conductive means connecting said second contact point of said third switch to said first terminal of said third relay; and electrically conductive means connecting said second terminal of said third relay to ground whereby when an off color object is detected a motor may be actuated to operate upon the object. 